Printing system and scheduling method

ABSTRACT

A method is provided for scheduling in a printing system comprising a plurality of modules. In the method, a print job comprising one or more sheet to be printed is submitted to the printing system. Available paths are determined for one of the one or more sheets of the print job. A preferred available path for said one of the one or more sheets of the print job is determined from the available paths. The preferred available path for said one of the one or more sheets of the print job is submitted to one or more of the plurality of modules. A reservation matrix representative of said one of the one or more sheets being scheduled on the preferred available path is updated. The steps of determining the available paths, determining a preferred available path, submitted the preferred available path and updating the reservation matrix are repeated for each subsequent sheet of the one or more sheets of the print job. A printing system comprising a plurality of modules is also provided. The printing system includes a data source having image data which is to be printed on one or more print media sheets and a scheduler linked to the data source and the modules for scheduling processing of the one or more print media sheets through the modules.

BACKGROUND

The present exemplary embodiment relates generally to a printing systemcomprising at least two marking engines and, more particularly, to ascheduling system and method for use in conjunction with a printingsystem comprising at least two marking engines. It finds particularapplication in conjunction with scheduling sheets of print jobs in amulti-marking engine printing system for maximizing output of theprinting system and will be described with particular reference thereto.However, it is to be appreciated that the present exemplary embodimentis also amenable to other like applications.

In a typical xerographic marking engine, such as a copier, printer,combination copier/printer, etc., a photoconductive insulating member ischarged to a substantially uniform potential and thereafter exposed to alight image representative of a document to be produced. This exposuredischarges the photoconductive insulating surface in exposed orbackground areas and creates an electrostatic latent image on themember, corresponding to image areas of the document to be produced.Subsequently, the electrostatic latent image on the photoconductiveinsulating surface is made visible by developing the image withdeveloping powder referred to in the art as toner. This developed imagemay be subsequently transferred to a print medium, such as a sheet ofcopy paper, to which it may be permanently affixed by heating and/or bythe application of pressure, i.e., fusing.

Electronic printing systems, including those that employ one or morexerographic marking engines as generally described above, can sometimesemploy a scanner for scanning image-bearing documents, i.e., sourcedocuments, and conversion electronics for converting an image scannedfrom a source document to image signals or pixels. Alternatively, imagesignals or pixels representative of an image or document to be printedcan be generated directly on a computer or like device, without the needfor a source document. In either case, the signals are typically storedand read out successively to the printing system for formation of theimages on photoconductive output media, such as a photoreceptor, andultimately transfer to a support substrate, such as described above.

A common trend in the maintenance of office equipment, particularlycopiers and printers, is to organize the printing system on a modularbasis, wherein certain distinct subsystems of the printing system arebundled together into modules which can be readily removed and replacedwith new modules, often of the same type. For example, the printingsystem could comprise two or more marking engine modules and a finishermodule. Modular designed printing systems facilitate greater flexibilityin terms of replacement and repair, and can even allow repairs ofindividual modules to take place at remote locations withoutnecessitating disabling of the entire printing system.

Incorporated by reference, by way of background and where appropriate,are the following references relating to what have been variously called“tandem engine” printers, “cluster printing,” “output merger” and thelike: U.S. Pat. No. 4,579,446; U.S. Pat. No. 4,587,532; U.S. Pat. No.5,272,511; U.S. Pat. No. 5,568,246; U.S. Pat. No. 5,570,172; U.S. Pat.No. 5,995,721; U.S. Pat. No. 5,596,416; U.S. Pat. No. 6,402,136; U.S.patent application Ser. No. 10/785,211 by Lofthus, et al., filed Feb.24, 2004 and entitled UNIVERSAL FLEXIBLE PLURAL PRINTER TO PLURALFINISHER SHEET INTEGRATION SYSTEM; U.S. patent application Ser. No.10/860,915 by Lofthus, et al., filed Jun. 3, 2004 and entitled UNIVERSALFLEXIBLE PLURAL PRINTER TO PLURAL FINISHER SHEET INTEGRATION SYSTEM; a1991 “Xerox Disclosure Journal” publication of November-December 1991,Vol. 16, No. 6, pp. 381-383; and the Xerox Aug. 3, 2001 “TAX”publication product announcement entitled “Cluster Printing SolutionAnnounced.”

Printing systems employing multiple print engines often enable higherprint speeds or print rates than heretofore realized by grouping aplurality of print engines together. These systems have been found to bevery cost competitive and provide an additional advantage over singleengine systems as a result of their inherent redundancy. For example, ifone print engine fails or is unusable, the printing system is still ableto function, possible at a reduced output rate, by using the remainingprint engine or engines. One challenge in these systems is scheduling ofprint jobs and, more particularly, scheduling of individual sheets ofprint jobs through the various modules, including multiple modules eachincluding a print engine, in an organized and efficient manner.

Various methods of scheduling print jobs and print media sheets of printjobs in a printing system employing multiple print engines are known.For example, U.S. Pat. No. 5,095,342 to Rarrell et al.; U.S. Pat. No5,095,369 to Ortiz; U.S. Pat. No. 5,159,395 to Farrell; U.S. Pat. No.5,557,367 to Yang et al.; U.S. Pat. No. 6,097,500 to Fromherz; U.S. Pat.No. 6,618,167 to Shah; 6,836,339 to Purvis et al.; and U.S. Pat. No.6,850,336 to Purvis et al.; U.S. patent application Ser. No. 10/924,458to Lofthus et al.; and U.S. patent application Ser. Nos. 20/384,514;10/248,560; 10/284,561; and 10/424,322, all to Fromherz, all of whichare incorporated herein in their entireties by reference., discloseexemplary scheduling systems. In particular, the '339 patent and the'336 patent disclose a scheduler for a printing machine to schedule theprocessing of sheets through the several modules of the printingmachine.

CROSS-REFERENCE TO RELATED APPLICATION(S)

The following applications, the disclosures of each being totallyincorporated herein by reference are mentioned:

U.S. Provisional Application Ser. No. 60/631,651 (Attorney Docket No.20031830-US-PSP), filed Nov. 30, 2004, entitled “TIGHTLY INTEGRATEDPARALLEL PRINTING ARCHITECTURE MAKING USE OF COMBINED COLOR ANDMONOCHROME ENGINES,” by David G. Anderson, et al.;

U.S. Provisional Patent Application Ser. No. 60/631,918 (Attorney DocketNo. 20031867-US-PSP), filed Nov. 30, 2004, entitled “PRINTING SYSTEMWITH MULTIPLE OPERATIONS FOR FINAL APPEARANCE AND PERMANENCE,” by DavidG. Anderson et al.;

U.S. Provisional Patent Application Ser. No. 60/631,921 (Attorney DocketNo. 20031867Q-US-PSP), filed Nov. 30, 2004, entitled “PRINTING SYSTEMWITH MULTIPLE OPERATIONS FOR FINAL APPEARANCE AND PERMANENCE,” by DavidG. Anderson et al.;

U.S. application Ser. No. 10/761,522 (Attorney Docket A2423-US-NP),filed Jan. 21, 2004, entitled “HIGH RATE PRINT MERGING AND FINISHINGSYSTEM FOR PARALLEL PRINTING,” by Barry P. Mandel, et al.;

U.S. application Ser. No. 10/785,211 (Attorney Docket A3249P1-US-NP),filed Feb. 24, 2004, entitled “UNIVERSAL FLEXIBLE PLURAL PRINTER TOPLURAL FINISHER SHEET INTEGRATION SYSTEM,” by Robert M. Lofthus, et al.;

U.S. application Ser. No. 10/881,619 (Attorney Docket A0723-US-NP),filed Jun. 30, 2004, entitled “FLEXIBLE PAPER PATH USINGMULTIDIRECTIONAL PATH MODULES,” by Daniel G. Bobrow.;

U.S. application Ser. No. 10/917,676 (Attorney Docket A3404-US-NP),filed Aug. 13, 2004, entitled “MULTIPLE OBJECT SOURCES CONTROLLED AND/ORSELECTED BASED ON A COMMON SENSOR,” by Robert M. Lofthus, et al.;

U.S. application Ser. No. 10/917,768 (Attorney Docket 20040184-US-NP),filed Aug. 13, 2004, entitled “PARALLEL PRINTING ARCHITECTURE CONSISTINGOF CONTAINERIZED IMAGE MARKING ENGINES AND MEDIA FEEDER MODULES,” byRobert M. Lofthus, et al.;

U.S. application Ser. No. 10/924,106 (Attorney Docket A4050-US-NP),filed Aug. 23, 2004, entitled “PRINTING SYSTEM WITH HORIZONTAL HIGHWAYAND SINGLE PASS DUPLEX,” by Lofthus, et al.;

U.S. application Ser. No. 10/924,113 (Attorney Docket A3190-US-NP),filed Aug. 23, 2004, entitled “PRINTING SYSTEM WITH INVERTER DISPOSEDFOR MEDIA VELOCITY BUFFERING AND REGISTRATION,” by Joannes N. M. deJong,et al.;

U.S. application Ser. No. 10/924,458 (Attorney Docket A3548-US-NP),filed Aug. 23, 2004, entitled “PRINT SEQUENCE SCHEDULING FORRELIABILITY,” by Robert M. Lofthus, et al.;

U.S. application Ser. No. 10/924,459 (Attorney Docket No. A3419-US-NP),filed Aug. 23, 2004, entitled “PARALLEL PRINTING ARCHITECTURE USINGIMAGE MARKING ENGINE MODULES (as amended),” by Barry P. Mandel, et al;

U.S. application Ser. No. 10/933,556 (Attorney Docket No. A3405-US-NP),filed Sep. 3, 2004, entitled “SUBSTRATE INVERTER SYSTEMS AND METHODS,”by Stan A. Spencer, et al.;

U.S. application Ser. No. 10/953,953 (Attorney Docket No. A3546-US-NP),filed Sep. 29, 2004, entitled “CUSTOMIZED SET POINT CONTROL FOR OUTPUTSTABILITY IN A TIPP ARCHITECTURE,” by Charles A. Radulski et al.;

U.S. application Ser. No. 10/999,326 (Attorney Docket 20040314-US-NP),filed Nov. 30, 2004, entitled “SEMI-AUTOMATIC IMAGE QUALITY ADJUSTMENTFOR MULTIPLE MARKING ENGINE SYSTEMS,” by Robert E. Grace, et al.;

U.S. application Ser. No. 10/999,450 (Attorney Docket No.20040985-US-NP), filed Nov. 30, 2004, entitled “ADDRESSABLE FUSING FORAN INTEGRATED PRINTING SYSTEM,” by Robert M. Lofthus, et al.;

U.S. application Ser. No. 11/000,158 (Attorney Docket No.20040503-US-NP), filed Nov. 30, 2004, entitled “GLOSSING SYSTEM FOR USEIN A TIPP ARCHITECTURE,” by Bryan J. Roof;

U.S. application Ser. No. 11/000,168 (Attorney Docket No.20021985-US-NP), filed Nov. 30, 2004, entitled “ADDRESSABLE FUSING ANDHEATING METHODS AND APPARATUS,” by David K. Biegelsen, et al.;

U.S. application Ser. No. 11/000,258 (Attorney Docket No.20040503Q-US-NP), filed Nov. 30, 2004, entitled “GLOSSING SYSTEM FOR USEIN A TIPP ARCHITECTURE,” by Bryan J. Roof;

U.S. application Ser. No. 11/001,890 (Attorney Docket A2423-US-DIV),filed Dec. 2, 2004, entitled “HIGH RATE PRINT MERGING AND FINISHINGSYSTEM FOR PARALLEL PRINTING,” by Robert M. Lofthus, et al.;

U.S. application Ser. No. 11/002,528 (Attorney Docket A2423-US-DlV1),filed Dec. 2, 2004, entitled “HIGH RATE PRINT MERGING AND FINISHINGSYSTEM FOR PARALLEL PRINTING,” by Robert M. Lofthus, et al.;

U.S. application Ser. No. 11/051,817 (Attorney Docket 20040447-US-NP),filed Feb. 4, 2005, entitled “PRINTING SYSTEMS,” by Steven R. Moore, etal.;

U.S. application Ser. No. 11/069,020 (Attorney Docket 20040744-US-NP),filed Feb. 28, 2004, entitled “PRINTING SYSTEMS,” by Robert M. Lofthus,et al.;

U.S. application Ser. No. 11/070,681 (Attorney Docket 20031659-US-NP),filed Mar. 2, 2005, entitled “GRAY BALANCE FOR A PRINTING SYSTEM OFMULTIPLE MARKING ENGINES,” by R. Enrique Viturro, et al.;

U.S. application Ser. No. 11/081,473 (Attorney Docket 20040448-US-NP),filed Mar. 16, 2005, entitled “PRINTING SYSTEM,” by Steven R. Moore;

U.S. application Ser. No. 11/084,280 (Attorney Docket 20040974-US-NP),filed Mar. 18, 2005, entitled “SYSTEMS AND METHODS FOR MEASURINGUNIFORMITY IN IMAGES,” by Howard Mizes;

U.S. application Ser. No. 11/089,854 (Attorney Docket 20040241-US-NP),filed Mar. 25, 2005, entitled “SHEET REGISTRATION WITHIN A MEDIAINVERTER,” by Robert A. Clark et al.;

U.S. application Ser. No. 11/090,498 (Attorney Docket 20040619-US-NP),filed Mar. 25, 2005, entitled “INVERTER WITH RETURN/BYPASS PAPER PATH,”by Robert A. Clark;

U.S. application Ser. No. 11/090,502 (Attorney Docket 20031468-US-NP),filed Mar. 25, 2005, entitled IMAGE QUALITY CONTROL METHOD AND APPARATUSFOR MULTIPLE MARKING ENGINE SYSTEMS,” by Michael C. Mongeon;

U.S. application Ser. No. 11/093,229 (Attorney Docket 20040677-US-NP),filed Mar. 29, 2005, entitled “PRINTING SYSTEM,” by Paul C. Julien;

U.S. application Ser. No. 11/095,872 (Attorney Docket 20040676-US-NP),filed Mar. 31, 2005, entitled “PRINTING SYSTEM,” by Paul C. Julien;

U.S. application Ser. No. 11/094,864 (Attorney Docket 20040971-US-NP),filed Mar. 31, 2005, entitled “PRINTING SYSTEM,” by Jeremy C. deJong, etal.;

U.S. application Ser. No. 11/095,378 (Attorney Docket 20040446-US-NP),filed Mar. 31, 2005, entitled “IMAGE ON PAPER REGISTRATION ALIGNMENT,”by Steven R. Moore, et al.;

U.S. application Ser. No. 11/094,998 (Attorney Docket 20031520-US-NP),filed Mar. 31, 2005, entitled “PARALLEL PRINTING ARCHITECTURE WITHPARALLEL HORIZONTAL PRINTING MODULES,” by Steven R. Moore, et al.;

U.S. application Ser. No. 11/102,899 (Attorney Docket 20041209-US-NP),filed Apr. 8, 2005, entitled “SYNCHRONIZATION IN A DISTRIBUTED SYSTEM,”by Lara S. Crawford, et al.;

U.S. application Ser. No. 11/102,910 (Attorney Docket 20041210-US-NP),filed Apr. 8, 2005, entitled “COORDINATION IN A DISTRIBUTED SYSTEM,” byLara S. Crawford, et al.;

U.S. application Ser. No. 11/102,355 (Attorney Docket 20041213-US-NP),filed Apr. 8, 2005, entitled “COMMUNICATION IN A DISTRIBUTED SYSTEM,” byMarkus P. J. Fromherz, et al.;

U.S. application Ser. No. 11/______ (Attorney Docket 20041214-US-NP),filed Apr. 8, 2005, entitled “ON-THE-FLY STATE SYNCHRONIZATION IN ADISTRIBUTED SYSTEM,” by Haitham A. Hlndi;

U.S. application Ser. No. 11/109,558 (Attorney Docket 19971059-US-NP),filed Apr. 19, 2005, entitled “SYSTEMS AND METHODS FOR REDUCING IMAGEREGISTRATION ERRORS,” by Furst et al.;

U.S. application Ser. No. 11/109,566 (Attorney Docket 20032019-US-NP),filed Apr. 19, 2005, entitled “MEDIA TRANSPORT SYSTEM,” by Mandel etal.;

U.S. application Ser. No. 11/109,996 (Attorney Docket 20040704-US-NP),filed Apr. 20, 2005, entitled “PRINTING SYSTEMS,” by Mongeon et al.; and

U.S. application Ser. No. 11/______ (Attorney Docket 20040656-US-NP),Filed Apr. 27, 2005, entitled “IMAGE QUALITY ADJUSTMENT METHOD ANDSYSTEM,” by Grace.

BRIEF DESCRIPTION

In one exemplary embodiment, a method is provided for scheduling in aprinting system comprising a plurality of modules. In the method, aprint job comprising one or more sheet to be printed is submitted to theprinting system. Available paths are determined for one of the one ormore sheets of the print job. A preferred available path for said one ofthe one or more sheets of the print job is determined from the availablepaths. The preferred available path for said one of the one or moresheets of the print job is submitted to one or more of the plurality ofmodules. A reservation matrix representative of said one of the one ormore sheets being scheduled on the preferred available path is updated.The steps of determining the available paths, determining a preferredavailable path, submitted the preferred available path and updating thereservation matrix are repeated for each subsequent sheet of the one ormore sheets of the print job.

In another exemplary embodiment, a printing system is provided. Theprinting system includes at least two modules, including at least onemarking engine module. The printing system also includes a data sourcehaving image data which is to be printed on one or more print mediasheets and a scheduler which is linked to the data source and linked tothe at least two modules for scheduling processing of the one or moreprint media sheets through the at least two modules.

In still another exemplary embodiment, a xerographic system is provided.The xerographic system includes a first marking engine module whichapplies images to print media sheets and a second marking engine modulewhich also applies images to print media sheets. A scheduler is linkedto the first and second marking engine modules for receiving a print joband scheduling sheets of said print job through the first and secondmarking engine modules to minimize time of the sheets passing throughthe first and second marking engine modules.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of an image marking engine module.

FIG. 2 is a schematic view of a printing system comprising a pluralityof image marking engine modules, including the marking engine module ofFIG. 1.

FIG. 3 is a schematic view of the printing system of FIG. 2, showinginterconnected print media paths of the printing system.

FIG. 4 is a block diagram illustrating a method for scheduling in theprinting system of FIGS. 2 and 3.

DETAILED DESCRIPTION

Referring now to the drawings wherein the showings are for purposes ofillustrating one or more exemplary embodiments, a marking engine moduleis schematically depicted in FIG. 1 and generally indicated by referencenumeral 10. In one application, as will be described in more detailbelow, the marking engine module 10 can serve as a replaceablexerographic module in a printing system. The term “marking engine” isused in connection with the one or more exemplary embodiments discussedherein to generally refer to a device for applying an image to printmedia. The marking engine module 10 of FIG. 1 includes many of thehardware elements or components-employed in the creation of desiredimages by electrophotographical processes, as will be known andunderstood by those skilled in the art. In the illustrated embodiment,the marking engine module 10 includes a charge retentive surface member,such as rotating photoreceptor 12 in the form of a drum (alternatively,the rotating photoreceptor could be a belt or other rotating devicehaving a charge retentive surface).

As also known and understood by those skilled in the art, images can becreated on the photoreceptor 12 and ultimately transferred from thephotoreceptor 12 to print media, such as a sheet of paper. The term“print media” is used in connection with the one or more exemplaryembodiments discussed herein to generally refer to a usually flimsyphysical sheet of paper, plastic, or other suitable physical print mediasubstrate for images, whether precut or web fed. Disposed about thephotoreceptor 12 are various xerographic subsystems, including acleaning device or station 14, a charging station 16, an exposurestation 18, which forms a latent image on the photoreceptor 12, adeveloper 20 for developing the latent image by applying a toner theretoto form a toner image, a transferring unit, such as a transfer corotron22, which transfers the toner image thus formed to the print media, anda fuser 24, which fuses the transferred image to the print media. In theillustrated embodiment, the fuser 24 is adapted to apply at least one ofheat and pressure to the print media to physically and permanentlyattach the toner and optionally to provide a level of gloss to theprinted media. In any particular embodiment of an electrophotographicmarking engine module, there can be variations to that described above,such as, for example, additional corotrons, cleaning devices, or, in thecase of a color printer, multiple developers.

The xerographic subsystems 14,16,18,20,22,24 of the illustratedembodiment are controlled by a marking engine controller 26, such as aCPU. Though the controller 26 of the illustrated embodiment isschematically shown as a single unit, it is to be appreciated that thecontroller can be distributed throughout the marking engine module 10and formed of multiple remotely positioned components. For example,actuators forming the controller 26 can be located in or on thexerographic subsystems and thus the controller is not necessarilyphysically removed from or separate from other elements of the module10. In the illustrated embodiment, the marking engine controller 26 islinked to an input/output interface 28 and a memory 30, and may also belinked to other components known by those skilled in the art to beprovided with a marking engine module, such as, for example, a markingcartridge platform, a marking driver, a function switch, sensors (suchas an “out of paper” indicator), a self-diagnostic unit, all of whichcan be interconnected by a data/control bus.

While the illustrated embodiment shows an electrophotographic printermarking engine module and particular reference herein is made to module10 which includes an electrophotographic marking engine, suitablemarking engines/modules can alternatively include ink-jet printers,including solid ink printers, thermal head printers that are used inconjunction with heat sensitive paper, and other devices capable ofmarking an image on a substrate. It is to be appreciated that suchalternative marking engines/modules can, like module 10, also include aninput/output interface, a memory, a marking cartridge platform, amarking driver, a function switch, sensors, a controller and aself-diagnostic unit, all of which can be interconnected by adata/control bus. Additionally, it is to be appreciated that a singlemarking engine module, such as module 10, could include multiple markingengines, in alternate embodiments.

The illustrated marking engine module 10 further includes a print mediatray 32 suitable for holding print media, such as a stack 34 of precutprint media sheets. As is known and understood by those skilled in theart, print media sheets are fed, typically from the top of the stack 34,along sheet path 36 to the transfer station 22 for receiving the tonerimage and through the fuser 24 for having the toner image permanentlyattached thereto. Although not illustrated, it is to be appreciated thatthe marking engine module 10 could be configured to employ duplexoperations on a print media sheet, wherein the sheet could be invertedand then fed for recirculation back through the transfer station 22 andthe fuser 24 for receiving and permanently fixing a side two image tothe backside of that duplex sheet. It should also be appreciated thatmodule 10 need not be limited to a single print media tray, and couldalternatively have no tray wherein the module 10 could be fed by aseparate feeder module or could have two or more trays, such as traysfor holding print media sheets of varying types (e.g., sizes, material,etc.). In one exemplary example, module 10 and any other marking modulesassociated with module 10 in a particular printing system can be fedwith print media from a single and/or separate print media source, suchas a high speed paper feeder, having any number of print media trays, orthe multiple marking engine modules could be fed from several printmedia sources, in lieu o or in addition to the print media tray 32.

With additional reference to FIG. 2, an exemplary printing system 40 isshown including an input/output interface 42, a plurality of markingengine modules, including first marking engine module 10 and secondmarking engine module 44 in the illustrated embodiment, a transportmodule 46, a finisher module 48 and a common control system 50, allinterconnected by links 52. These links 52 can be wired or wirelesslinks or other means or devices capable of supplying electronic data toand/or from the interconnected elements. For example, the links 52 canbe telephone lines, computer cables, ISDN lines, wireless communicationmeans or links (e.g., employing Bluetooth® wireless technology) and thelike. While FIG. 2 illustrates an embodiment employing two markingengine modules 10,44, both of which can be similarly configured (i.e.,the marking engine module 44 can be like the marking engine module 10),it is to be appreciated that the printing system 40 could include only asingle marking engine module or could include more than two modules,such as three, four, five, six, or eight marking engine modules. Likemarking module 10, the second marking module 44 includes a second moduleinput/output interface 54 linked to a second module controller 56 and asecond module memory 58, as well as a print media tray 60 for holding astack 62 of print media sheets to be delivered along sheet path 64 toprinter drum 66.

As will be described in more detail below, the transport module 46 linksor connects the sheet paths 36,64 of the marking engine modules 10,44 tothe finisher module 48. In an exemplary embodiment, the transport module46 is a transport system including a network of flexible print mediapathways that collect print media from each of the print modules 10,44and deliver the collected print media to the finisher module 48. Thetransport module 46 can include an input/output interface 68 linked to atransport module controller 70 and a transport module memory 72. Thetransport system of the transport module 46 can comprise drive membersor rollers, spherical nips, air jets, or the like (not shown) for movingprint media sheets received from the marking engine modules 10,44 to thefinisher module 48. The transport system can further include associatedmotors for the drive members, belts, guide rods, frames, etc. (notshown), which, in combination with the drive members, serve to conveythe print media along selected pathways at selected speeds.

As described in more detail below, the paths or pathways 74,78 (see FIG.3) of the transport module 46 allow print media sheets marked by two ormore marking engine modules, such as modules 10,44, to be assembled in acommon stream and delivered to a finisher module, such as module 48. Itwill be appreciated that the marking engine modules employed in theprinting system 40, including modules 10,44, can be configured forduplex or simplex printing and that a single sheet of print media can bemarked by two or more of the marking engine modules or marked aplurality of times by the same marking engine module, for example, byproviding internal duplex pathways. The details of practicing parallelsimplex printing and duplex printing through tandemly arranged markingengine modules are known and can be generally appreciated with referenceto the foregoing cited U.S. Pat. No. 5,568,246.

The finisher module 48 receives pint media sheets passing through thetransport module 46, typically already assembled in a common stream bythe transport module 46. The term “finisher” or “finishing module” asbroadly used herein in connection with the exemplary embodiment orembodiments disclosed herein, is any post-printing accessory device suchas an inverter, reverter, sorter, mailbox, inserter, interposer, folder,stapler, collator, stitcher, binder, over-printer, envelope stuffer,postage machine, output tray, or the like. In the illustratedembodiment, the finisher module 48 includes an output tray 80 (FIG. 3)to which received print media sheets can be delivered along path 82, aswell as an input/output interface 84 linked to a finisher controller 86and a finisher memory 88. The finisher module 48 can provide variousfinishes to the print media sheets of a print job or jobs, or even aportion of a print job. Finishes can include, for example, patterns ofcollation, binding or stapling available by the finisher module.Additional, advanced finishes can include, for example, other bindingtechniques, shrink wrapping, various folding formats, etc. The finishermodule 46 can also be provided with multiple output trays (not shown)and the ability to deliver specified print media sheets to a selectedoutput tray or trays.

With continued reference to FIG. 2, a data source 90, such as acomputer, network device or scanner can serve as an image input devicefor the printer system 40 in the illustrated embodiment. In one example,the data source 90 can be a computer network which is used to generateor acquire image signals or pixels and create print jobs therefrom. Inanother example, such as when on-site image input is desirable, the datasource 90 could be or include a scanner which can be used by a user ofthe printer system 40 to scan image-bearing documents, i.e., sourcedocuments. The scanner can include or be used in conjunction withconversion electronics for converting an image scanned from a sourcedocument or documents to image signals or pixels and ultimately createprint jobs therefrom.

Other sources of image data, each capable of serving as the data source90, are also contemplated, including floppy discs, hard discs,transportable memory devices, such as flash memory and the like, or anyelectronic storage medium or device capable of supplying image data. Ofcourse, as will be understood and appreciated by those skilled in theart, the data source 90 need not be limited to a single data source, butcould be a plurality of image input devices. For example, the datasource could be or include both a network and a scanner. As is known bythose skilled in art, the data source 90, whatever its configuration,can additionally be connected or linked to other networks and/orcomputers (not shown), or other data sources. For example, the datasource 90 can be a network server connected or linked to one or moreworkstations, such as personal computers.

A print job, including the image data of the data source 90, is created,either upstream of the printing system 40 or in the printing system 40itself. Typically, the print job includes the image data in the form ofa plurality of electronic pages and a set of processing instructions.The term “print job” is used in connection with the one or moreexemplary embodiments discussed herein to generally refer to a set ofrelated sheets to be printed, usually one or more collated copy setscopied from a set of original document sheets or electronic documentpage images, from a particular user, or which are otherwise related.Each print job can, for example, include the number of print mediasheets to be printed on, the size and type of each print media sheet tobe printed on, whether simplex or duplex printing is required, etc. U.S.Pat. No. 5,710,635 to Webster, incorporated herein by reference,describes a representation of an example print job or document and howthat representation can be transformed into something the printingsystem 40 can use to print the job. U.S. Pat. No. 5,604,600 to Websterand U.S. Pat. No. 5,129,639 to DeHority, both incorporated herein byreference, further describe example print job processing.

The control system 50 further includes a scheduling system 92 and aprint media path controller 94. The scheduling system 92 schedules theprinting of a print job including selection of the marking enginemodules to be used (10 or 44 in the illustrated embodiment) and theroute of each sheet of the print job through the system 40. As will bedescribed in more detail below, the scheduling system 82 receives one ormore print jobs, such as described above and including the image data ofthe data source 90, or at least the scheduling system 82 receivesinformation corresponding to the one or more print jobs, and therefromschedules sheets of the one or more print jobs through the modules10,44,46,48 of the printing system 40 based on various constraints, suchas optimizing the output of the printing system 40. While the operationsof the scheduling system 92 are herein described with reference to asingle job, it will be appreciated that the scheduling system canconsider several print jobs in a queue and can schedule printing ofprint jobs from the queue contemporaneously or in an optimum sequence tooptimize throughput of the printing system 40 or other variables, suchas image quality.

The print media path controller 94 routes the sheets through the system,as well as controls the switch positions through the modules in order toexecute a print job stream. Specifically, as will be described in moredetail below, the print media path controller 94 routes sheets of printmedia through the system 40 as instructed by the scheduling system 92. Auser or operator of the system 40 can communicate with the controlsystem 50 by means of a communication station 96, which can be a touchscreen, keypad and display screen, keyboard and monitor or the like.

FIG. 3 schematically illustrates the printing system 40 of FIG. 2 toshow the interconnected print media paths 36,64,74,78,82 through andbetween the assembled modules 10,44,46,48. In the exemplary printingsystem 40 of FIG. 3, the marking engine modules 10,44 are shown linkedfor parallel printing of print media sheets within the system and thetransport module 46 is shown connected to the marking modules 10,44 forreceiving printed on print media sheets and delivering these to thefinisher module 48. Specifically, transport module path 74 connectsfirst marking module path 36 to the finisher path 82 and transportmodule path 78 connects second marking module path 64 to the finisherpath 82.

In operation, with additional reference to FIG. 4, each of one or moremodules reports its availability to the control system 50 and, morespecifically, the scheduling system 92, also referred to herein as ascheduler 92 (step S100). In the illustrated embodiment, all of themodules 10,44,46,58 individually report whether they are available tothe scheduler 92. Reporting of availability could occur when theprinting system 40 is first switched on (i.e., powered up) and/or couldoccur on a continuing basis as the printing system 40 is operated. Forexample, controller 26 of print engine module 10 could report thatmodule 10 is switched off, out of paper, jammed, etc. to indicate thatmodule 10 is unavailable.

Each of the one or more modules also reports its print media processingparameters to the control system 50 and, more specifically, thescheduler 92 (step S102). Processing parameters can relate to printmedia sheet processing parameters, including, for example, process speed(i.e., the transit speed, such as mm/s, of sheets traveling in aparticular module), sheet transit time (i.e., the elapsed or overalltime for a sheet to travel in a module), and pitch period (i.e., theminimum delay or amount of time required between sheets traveling in amodule, such as may be needed for sheet tracking sensors to functionproperly). One or more of the processing parameters can be dependentupon the print media sheet traveling in a module. For example, printmedia sheets of varying lengths will likely have varying sheet transittimes in a particular module. Like step S100, step S102 can occur at anytime, such as during initial boot-up or on a continuing basis. When aprocessing parameter is sheet type specific, step S102 may not be ableto occur prior to the module determining what sheet is being used. Theprocessing parameters of each module can be stored in the module'smemory (e.g., memory 30 of module 10) and/or derived from the module'scontroller (e.g., controller 26 of module 10).

At some point, a user will submit a print job, or information that willform or correspond to a print job, to the printing system 40 and thescheduler 92 will receive the print job, or said information forming orcorresponding to the print job (step S104). The step of the scheduler 92receiving the print job need not occur after steps S100 and/or S102, butcould occur at any time. As described above, the print job indicates thenumber of sheets to be printed and possibly specified types of sheets onwhich the printing system 40 is to print. Alternatively, thisinformation can be derived from the print job or informationcorresponding to the print job.

Once a print job is received, the scheduler 92 establishes the availablepaths through the printing system 40 for sheet or sheets of the printjob (step S106). In the illustrated method, the scheduler 92 initiallyestablishes the available paths through the printing system 40 of aselected sheet of the print job, such as the first sheet of the printjob. Establishing the available paths can be dependent upon whichmodules are available (reported in step S100), the particular printmedia processing parameters of each module (reported in step S102),and/or the requirements or instructions associated with each sheet to beprinted in the print job. For example, if the print job specifies that aparticular sheet is to printed on a particular size of paper, only pathsstemming from a tray capable of delivering the desired paper size willbe established as being available. In another example, if the print jobspecifies that a particular sheet is to be printed on two sides, onlypaths passing through print engine modules which have reported two-sidedprinting capabilities will be established as being available.

After determining or establishing the available paths, the scheduler 92determines or calculates the most appropriate or preferred path of theavailable paths (step S108). In one exemplary embodiment, the preferredpath is the path which gets a particular sheet of print media to thefinisher module 48 in the least amount of time, i.e., the fastestavailable path. As described in more detail below, calculating thepreferred path of the available paths (step S108) can require thescheduler 92 to consult or lookup a reservation matrix which indicateswhen particular modules or paths will be available based on previouslyscheduled print media sheets. Calculating the preferred path can bedependent upon the particular print media processing parameters of eachmodule (reported to the scheduler 92 in step S102). For example, thetransit time and the pitch period of a first module through which afirst available path passes may be shorter than the transit time andpitch period of a second module through which a second available pathpasses, in which case the first available path might be preferred wherespeed is desirable.

After calculating the preferred path of the available paths, thescheduler 92 submits the calculated path to the modules (step S110) andupdates the reservation matrix (step S112). More particularly, uponcalculation of the preferred path, an itinerary is generated for theprint media sheet to be processed along the preferred path. The sheet'sitinerary, which is information representative of the path calculated asthe preferred path and the time at which the print media sheet is to besent along the preferred path, is submitted to the modules. In oneexemplary embodiment, the sheet's itinerary is sent only to modulestasked with processing the print media sheet and/or the print media pathcontroller 94 sends the itinerary to the modules. In any case, themodules receiving the itinerary are able to use it to determine when theprint media corresponding to the itinerary is to be processed. Forexample, a module, such as module 44, could receive a sheet itineraryand store it in its memory, such as memory 58, or the itinerary could befirst directed to the controller, such as controller 56.

The step of updating the reservation matrix (S112) occurs so thatsubsequently processed sheets, i.e., sheets that are to be scheduledthrough the printing system 40, can be scheduled in view of the alreadyscheduled print media sheet. For example, if a first of two availablepaths is determined to be the preferred or fastest path for a firstprint media sheet, the first path may not be the preferred or fastestpath for a second, subsequent print media sheet because the first pathmay be occupied with processing the first print media sheet.Accordingly, a reservation matrix is stored by the scheduler 92, whichdetails when each module or path will be open for a subsequentlyprocessed print media sheet. The reservation matrix can be reviewed orconsulted by the scheduler 92 when processing (i.e., calculating apreferred path in step S108) for subsequently processed print mediasheets.

After updating the reservation matrix, in step S114, if more sheetsremain in a print job being processed or in a subsequently submittedprint job, steps S106 through S114 are repeated for subsequent sheet orsheets. More specifically, step S106 is returned to and the availablepaths are again established for the additional sheets to be processed.After establishing the available paths for the subsequent sheet, thescheduler 92 again determines the preferred available path (S108), butfor the subsequent sheet. Determining the preferred available path forthe subsequent sheet takes into account the already scheduled itineraryof the already scheduled sheet. More specifically, the scheduler 92consults the reservation matrix, which indicates when certain pathsand/or modules will be available in view of the already scheduled sheet.Thus, when the preferred path is determined for the subsequent sheet,the preferred path is calculated while taking account for the processingof the earlier scheduled sheet. Upon determining the preferred path forthe subsequent sheet, the scheduler 92 submits this path to the modules(S110) and updates the reservation matrix to reflect scheduling of thesubsequent sheet (S112). The steps (S106-S114) repeat until all sheetsare processed.

The scheduling system or scheduler 92 herein described can beimplemented either on a single program general purpose computer or aseparate program general purpose computer. However, the schedulingsystem 92 can also be implemented on a special purpose computer, aprogrammed microprocessor or microcontroller and peripheral integratedcircuit element, an ASIC, or other integrated circuit, a digital signalprocessor, a hardwired electronic or logic circuit such as a discreteelement circuit, a programmable logic device such as a PLD, PLA, FPGA,PAL, or the like. In general, any device, capable of implementing afinite state machine that is in turn capable of implementing thescheduler-related steps in the flowchart of FIG. 4 can be used toimplement the scheduling system 92.

The disclosed method can be readily implemented in software using objector object-oriented software development environments. Alternatively, thedisclosed scheduling system 92 can be implemented partially or fully ina hardware using standard logic circuits or VLSI design. Whethersoftware or hardware is used to implement the system 92 in accordancewith the exemplary embodiments is dependent, at least in part, on thespeed and/or efficiency requirements of the system, the particularfunction, and the particular software or hardware systems ormicroprocessors or microcomputer systems being utilized. The schedulingsystem 92 and methods described herein, however, can be readilyimplemented in hardware or software using any suitable systems orstructures, devices and/or software known by those skilled in theapplicable art without undue experimentation from the functionaldescription provided herein together with a general knowledge of thecomputer arts.

An example application of the method of FIG. 4 will now be described inconnection with the illustrated print system 40 of FIGS. 2 and 3. Asshown in FIGS. 2 and 3, the printing system 40 includes four modules10,44,46,48. In step S100, according to the example, each module10,44,46,48 reports that it is available. In step S102, according to theexample, each module 10,44,46,48 reports its print media processingparameters. More specifically, in this example, each module 10,44,46,48reports that it has a path or paths and reports the transit time (t) andpitch period (p) associated with each reported path.

More specifically, the marking engine modules 10,44 each report thatthey have a path available, path 36 on module 10 and path 64 on module44, and report transit times and pitch periods associated, respectively,with paths 36,64. Likewise, the finisher module 48 reports that it haspath 82 and reports a transit time and pitch period associatedtherewith. Transport module 46 reports that it has paths 74 and 78 andreports a transit time and pitch period associated with each path 74 and78. In one exemplary example, the reported print media processingparameters are as in TABLE 1. TABLE 1 Transit Time Pitch Period Path(seconds) (seconds) first marking module path 36 1.8 0.9 second markingmodule path 64 1.7 0.9 transport module path 74 3.2 0.5 transport modulepath 78 1.6 0.5 finisher module path 82 1.9 0.5

When a print job is submitted, the print job is received by thescheduler 92 (S104). In the exemplary example, the print job indicatesthat three (3) sheets are to printed in simplex form (i.e., one sideonly). Next, the scheduler establishes the available paths through theprinting system 40, based on the print media processing parameters andthe print job being processed. In the exemplary example, the three (3)sheets of the print job are available from either print media tray 34 or62 and can be printed on by either marking engine module 10 or 44. Thus,the total count of available paths through the print system 40 is two(2), including a first print system path, comprising module paths 36,74and 82, and a second print system path, comprising module paths 64,78and 82.

Next, the scheduler 92 determines the preferred available path (S106).In the example herein discussed, the preferred path is that which candeliver a print media sheet to the output tray 80 faster. Thus, thescheduler 92 determines the preferred available path, either first printsystem path 36,74,82 or second print system path 64,78,82, is the onethat can deliver the first sheet of the submitted three-sheet print jobto the output tray 80 of the finisher module 48 faster. When determiningthe preferred path, the scheduler 92 first consults the reservationmatrix to determine when specific modules will be available and therebydetermines the earliest time a sheet could be released from its tray ortrays, first module tray 32 or second module tray 60 in the printingsystem 40. In this example, the first sheet of the print job is thefirst sheet submitted to the scheduler 92, so no other sheets have yetbeen scheduled (alternatively, any previously scheduled sheets havealready been processed or printed, so no sheet itineraries remain in thescheduler 92). Accordingly, since no preexisting sheet itinerariesremain, the reservation matrix could be as indicated in TABLE 2. TABLE 2Path Available Path (seconds) first marking module path 36 T₀ secondmarking module path 64 T₀ transport module path 74 T₀ transport modulepath 78 T₀ finisher module path 82 T₀wherein T₀ is approximately the time in which the print job was receivedby the scheduler 92. Thus, according to the reservation matrix of thisexample, all of the paths are immediately available, as noreservations/itineraries have yet been made and/or remain in theprinting system 40.

Next, still in step S106, the scheduler calculates when the first sheetof the print job would be delivered to the finisher module 48 along eachof the available paths taking into consideration the earliest availablerelease times based on the reservation matrix, compares the calculationsfor each available path and selects the path which will result in thesheet arriving at the finisher module 48 the earliest (i.e., selects thepreferred path). In this example, the first printer system path 36,74,82would deliver the first sheet of the print job to the finisher module 48in 5 seconds (1.8 second transit time in module 10 and 3.2 secondtransit time in the transport module 46). The second printer system path64,78,82 would deliver the first sheet of the print job to the finishermodule 48 in 3.3 seconds (1.7 second transit time in module 44 and 1.6second transit time in transport module 46). No previous sheets havebeen scheduled so both paths, as indicated above, are available at T0.Accordingly, the scheduler 92 would select the second path 64,76,82 forthe first sheet of the print job.

Next, the scheduler 92 would submit the preferred available path to themodules (S110), including the arrival time and exit times for the firstsheet. For example, the first sheet would start in module 44 at T0,enter the transport module at T0+1.7 seconds (transit time throughmodule 44), and enter the finisher at T0+1.7 seconds+1.6 seconds(transit time through module 46). In one exemplary embodiment, only themodules 44,46,48 that are to process the print job receive informationfrom the scheduler 92. The scheduler 92 also updates the reservationmatrix (S112). After processing the first sheet of the print job, thereservation matrix could be as indicated in TABLE 3. TABLE 3 Path PathAvailable (seconds) first marking module path 36 T₀ second markingmodule path 64 T₀ + 0.9 transport module path 74 T₀ transport modulepath 78 T₀ + 1.7 + 0.5 = T₀ + 2.2 finisher module path 82 T₀ + 1.7 +1.6 + 0.5 = T₀ + 3.8

In other words, the second marking module 44 will be able to takeanother sheet in T0+0.9 (wherein 0.9 second is the pitch period for thesecond module 44). The first marking module 10, since it still does nothave a sheet schedule, can take a sheet as soon as the print jobarrives, likewise with the first transport module path 74. The secondtransport module path 78 can take another sheet after 2.2 seconds(includes 1.7 seconds transit time through second module 44 and 0.5seconds pitch period for the transport module). The finisher module 48can take a second sheet in 3.8 seconds, which includes transit timesthrough the second module 44 and the second path 78 of the transportmodule 46 (1.7 seconds for second module 44 and 1.6 seconds for path78), and a pitch period of 0.5 seconds for the finisher.

Because two more sheets remain to be processed in the example, step S114directs back to step S106, wherein the scheduler 92 determines allavailable paths for the second sheet of the three sheet print job. Asindicated above, both paths 36,74,82 and 64,78,82 are available for allsheets of the example print job. Next, the scheduler determines thepreferred available path for the second sheet of the print job (S108).Again, the earliest the second sheet could be released for each path iscalculated. Since the first path 36,74,82 has no sheets scheduled, asheet could be released from tray 32 in the first path at T0. As withthe first sheet, the first path could deliver a sheet to the finishermodule 48 in 5 seconds.

The second path 64,78,82 already has a sheet scheduled. Accordingly, theearliest the second sheet could be released from the tray 60 is themaximum of (1) when the second module path is free (0.9 seconds fromreservation matrix), (2) when the transport module second path 78 isfree less the transit time through the second module 44 (2.2 secondsfrom the reservation matrix−1.7 seconds transit time through secondmodule 44=0.5 seconds), and (3) when the finisher path 82 is free lessthe transit time through the modules 44,46 (3.8 seconds from reservationmatrix−1.6 seconds−1.7 seconds=0.5 seconds), or 0.9 seconds. Includingthe 0.9 second delay, the second sheet could be to the finisher in 4.2seconds, which is still less than the 5 seconds required to get thesecond sheet through the first path 36,74,82. Accordingly, the secondpath 64,78,82 is also selected for the second sheet of the print job.

Next, the scheduler 92 would submit the preferred available path for thesecond sheet to the modules (S110), including the arrival time and exittimes for the second sheet. The scheduler 92 also again updates thereservation matrix (S112). After processing the second sheet of theprint job, the reservation matrix could be as indicated in TABLE 4.TABLE 4 Path Path Available (seconds) first marking module path 36 T₀second marking module path 64 T₀ + 1.8 transport module path 74 T₀transport module path 78 T₀ + 3.1 finisher module path 82 T₀ + 4.7Specifically, the second module 44 would have another 0.9 second pitchperiod added increasing the previous value, T₀+0.9 seconds, to T₀+1.8seconds. Likewise, the transport module path 78 and the finisher modulepath 82 each have another 0.9 seconds pitch period added, respectively.The first module 10 and the first transport module path 74 are bothstill available at T₀. For the third sheet of the print job, the steps(S106-S112) are again repeated. This time, however, the first path36,74,82 is faster for delivering the third sheet to the finisher module48 and is selected as the preferred available path.

The exemplary embodiment has been described with reference to thepreferred embodiments. Obviously, modifications and alterations willoccur to others upon reading and understanding the preceding detaileddescription. It is intended that the exemplary embodiment be construedas including all such modifications and alterations insofar as they comewithin the scope of the appended claims or the equivalents thereof.

1. A method for scheduling in a printing system comprising a pluralityof modules, the method comprising: (a) submitting a print job comprisingone or more sheets to be printed to said printing system; (b)determining available paths for one of said one or more sheets of saidprint job; (c) determining a preferred available path for said one ofsaid one or more sheets of said print job from said available paths; (d)submitting said preferred available path for said one of said one ormore sheets of said print job to one or more of said plurality ofmodules; (e) updating a reservation matrix representative of said one ofsaid one or more sheets being scheduled on said preferred availablepath; (f) repeating steps (d) through (g) for each subsequent sheet ofsaid one or more sheets of said print job.
 2. The method of claim 1further including at least one of the steps of: reporting availabilityof each of said plurality of modules; and reporting print mediaprocessing parameters for each of said plurality of modules.
 3. Themethod of claim 2 wherein the step of determining said available pathsincludes the substep of: using one or more of (i) said availability ofsaid modules, (ii) said print media processing parameters of saidplurality of modules, and (iii) said print job to determine saidavailable paths.
 4. The method of claim 2 wherein the step of reportingprint media processing parameters includes reporting the print mediaprocessing parameters related to print media paths through said modules.5. The method of claim 4 wherein said print media processing parametersinclude one or more of (i) sheet transit time for each path through saidmodules; (ii) process speed for each path through said modules and (iii)pitch period for each path through said modules.
 6. The method of claim5 wherein said print media processing parameters are dependent upon saidone of said one or more sheets of said print job.
 7. The method of claim4 wherein said step of determining said preferred available path isdependent upon said print media processing parameters reported.
 8. Themethod of claim 1 wherein said plurality of modules includes at least afirst marking engine module and a second marking engine module.
 9. Themethod of claim 8 wherein said plurality of modules further includes atransport module and a finisher module.
 10. The method of claim 1wherein step (g) includes the substep of: determining a preferredavailable path for a second of said one or more sheets of said print jobfrom said available paths in view of said one of said one or more sheetsof said print job already being scheduled.
 11. The method of claim 1wherein said print job indicates the number of sheets to be printed andoptionally specified types of sheets on which said print job is to beprinted.
 12. The method of claim 1 wherein the step of determining saidpreferred available path includes determining which of said availablepaths will deliver said one of said one or more sheets of said print jobto an output tray of said printing system in the least amount of time.13. The method of claim 1 wherein said step of determining saidpreferred available path includes the substep of consulting saidreservation matrix to determine when each of said modules will beavailable based on any previously scheduled print media sheets in saidprinting system.
 14. The method of claim 1 wherein said step ofdetermining said preferred available path includes the substeps of:calculating when said one of said one or more sheets would be deliveredto an output tray along each of said available paths, including takinginto consideration the earliest available release times of each of saidmodules from said reservation matrix; comparing calculations of whensaid one of said one or more sheets would be delivered to said outputtray; and selecting said preferred available path as the path which willresult in said one of said one or more sheets being delivered to saidoutput tray the earliest.
 15. A printing system, comprising: at leasttwo modules, including at least one marking engine module; a data sourcehaving image data which is to be printed on one or more print mediasheets; and a scheduler linked to said data source and linked to said atleast two modules for scheduling processing of said one or more printmedia sheets through said at least two modules.
 16. The printing systemof claim 15 wherein said at least two modules includes at least twomarking engine modules.
 17. The printing system of claim 16 wherein saidat least two modules further includes at least one of a finisher moduleand a transport module.
 18. The printing system of claim 17 wherein afirst printing system path is defined through said at least two modulesand a second printing system path is defined through said at least twomodules, said scheduler configured to select said first printing systempath or said second printing system path for each of said one or moreprint media sheets for providing said one or more print media sheets tosaid finisher module in the least amount of time.
 19. The printingsystem of claim 15 wherein said scheduler includes a reservation matrixthat is updated as each of said one or more sheets is scheduled throughsaid at least two modules for recording when each of said at least twomodules will be available.
 20. A xerographic system, comprising: a firstmarking engine module which applies images to print media sheets; asecond marking engine module which applies images to print media sheets;and a scheduler linked to said first and second marking engine modulesfor receiving a print job and scheduling sheets of said print jobthrough said first and second marking engine modules to minimize time ofsaid sheets passing through said first and second marking enginemodules.